Self-monitoring of blood glucose (SMBG) is important for diabetic patients to manage their blood glucose levels and to use this monitoring in treatment. Simple blood glucose self-monitoring devices using an electrochemical biosensor have recently found wide use in SMBG. The biosensor includes an insulating substrate on which electrodes and an enzyme reaction layer are formed.
Examples of enzymes used herein include glucose dehydrogenase (GDH), glucose oxidase (GO), and the like. In terms of methods using GO (EC 1.1.3.4), a problem has been noted in that dissolved oxygen in a measurement sample is likely to affect the measurement results. Although GDH is unaffected by dissolved oxygen, it is not suitable for accurately measuring blood glucose levels, because, for example, a pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) (EC 1.1.5.2 (formerly EC 1.1.99.17)) acts on sugars such as maltose and lactose, in addition to glucose.
A flavin adenine dinucleotide-dependent glucose dehydrogenase (hereinafter also referred to as “FADGDH”) is known as a flavin-bound glucose dehydrogenase that is unaffected by dissolved oxygen and that has almost no action on maltose. For example, Patent Documents 1 to 5 report enzymes derived from Aspergillus terreus and Aspergillus oryzae, and modifications of these. These enzymes, however, have relatively high reactivity to xylose (Patent Document 1), and there is therefore room for improvement in accurately measuring the blood glucose of people who are undergoing a xylose tolerance test. Meanwhile, a flavin-bound GDH having relatively low action on xylose (Patent Document 6), a modified GDH having combined advantages of GO and GDH (Patent Document 7), and the like, have been developed, but there is still room for improvement.